The present invention relates to microelectronic device fabrication and, more particularly, to gate dielectrics for semiconductor devices.
In the fabrication of semiconductor devices, the semiconductor substrate undergoes a number of thermal processes some of which are performed in two separate apparatus. Batch furnaces, such as vertical diffusion furnaces (VDF), are capable of processing 100-200 substrate simultaneously and are used predominantly for well drive-ins, field oxidation, and gate oxidation of films thicker than about 100 nm. Rapid thermal processors (RTPs) process one wafer at a time and are used predominantly for silicidation, nitridation, SiO2 anneals, and gate oxidation for films under 100 nm.
In front-end processing, gate oxidation is usually considered the most critical oxidation application, as required gate oxide thickness"" shrink from 40-50 nm for the 0.25 xcexcm devices to 30-40 nm for 0.18 xcexcm devices and 20-30 nm for 0.15 xcexcm devices. Due to currently available batch furnace limitations, RTPs are used for the ultra-thin, below 100 nm, dielectric gate oxidation and nitridation.
Incorporating nitrogen into the gate oxide, known as nitridation, is an important step in fabrication of an ultra-thin gate dielectric. The incorporation of nitrogen degrades low-field electron mobility, increases high-field electron mobility, improves charge to breakdown, and increases fixed positive charge, among others.
Rapid thermal processors provide dedicated equipment that can provide the precise level of process control required for ultra-thin gate oxidation layers, and in particular, nitridation of the gate oxide. Rapid thermal processors provide faster temperature rise times and more precise temperature uniformity than batch furnaces, which provides the necessary control.
In order to increase through-put and reduce operating times and costs, it is desired to provide gate oxidation and nitridation in-situ and in sequence with other processes using the batch furnace. There is potential to reduce the number of thermal cycles, processing steps, and the cost of equipment if gate oxidation and nitridation can be performed in the batch furnace.
New apparatus and methods are needed for providing an ultra-thin nitrided gate dielectric in an in-situ process using a batch process.